Investigation of optical metastability in GaN using photoluminescence spectroscopy

We report photo-induced changes of optically active defects in GaN under 325 nm excitation. Cooling the sample in the dark and then performing rapid measurements using a Fourier transform spectrometer allows the changes in the spectrum to be followed on time scales of minutes. At first, the characteristic blue and yellow luminescence bands are observed, with the blue band roughly four times stronger than the yellow. Upon continuous irradiation the yellow band increases rapidly at first, and then more slowly to become the dominant band after approximately 60 min. During this time the blue band decreases. The temperature dependence of this fatigue behaviour is reported for both constant and intermittent illumination.